Electrified vehicle battery packs with improved thermal interface material distribution

ABSTRACT

This disclosure details exemplary battery pack designs for use in electrified vehicles. An exemplary battery pack assembly process may include supporting one or more components, such as a heat exchanger plate, of the battery pack against deflection during the assembly process. Supporting the heat exchanger plate to keep the plate relatively flat during the battery pack assembly process improves the flow distribution of a thermal interface material (TIM), thereby achieving improved TIM coverage and improved heat transfer between battery cells and the heat exchanger plate of the battery pack.

TECHNICAL FIELD

This disclosure relates to electrified vehicle battery packs, and moreparticularly to electrified vehicle battery packs that exhibit improvedthermal interface material (TIM) distribution by supporting a heatexchanger plate of the battery pack during the assembly process.

BACKGROUND

The desire to reduce automotive fuel consumption and emissions is welldocumented. Therefore, vehicles are being developed that reduce orcompletely eliminate reliance on internal combustion engines.Electrified vehicles are currently being developed for this purpose. Ingeneral, electrified vehicles differ from conventional motor vehiclesbecause they are selectively driven by one or more battery poweredelectric machines. Conventional motor vehicles, by contrast, relyexclusively on the internal combustion engine to propel the vehicle.

A high voltage traction battery pack typically powers the electricmachines and other electrical loads of the electrified vehicle. Thebattery pack includes a plurality of battery cells that store energy forpowering these electrical loads. The battery cells generate heat duringcharging and discharging operations. This heat must be dissipated inorder to achieve a desired level of battery performance Heat exchangerplates, often referred to as “cold plates,” may be used for dissipatingthe heat.

SUMMARY

A method according to an exemplary aspect of the present disclosureincludes, among other things, supporting a heat exchanger plate of abattery pack against deflection during an assembly process.

In a further non-limiting embodiment of the foregoing method, the heatexchanger plate is maintained substantially flat during the assemblyprocess.

In a further non-limiting embodiment of either of the foregoing methods,supporting the heat exchanger plate includes positioning a tray of thebattery pack against a rigid workstation and positioning the heatexchanger plate against the tray.

In a further non-limiting embodiment of any of the foregoing methods,the rigid workstation includes a convex surface in contact with a bottomof the tray.

In a further non-limiting embodiment of any of the foregoing methods,the convex surface contacts the bottom of the tray near a center of thetray.

In a further non-limiting embodiment of any of the foregoing methods,supporting the heat exchanger plate includes positioning a tray of thebattery pack against a rigid workstation, positioning a structuralmaterial such as a foam block within the tray, and positioning the heatexchanger plate within the tray such that the foam block is between thetray and the heat exchanger plate.

In a further non-limiting embodiment of any of the foregoing methods,rigidly supporting the heat exchanger plate includes positioning a foamblock within a tray of the battery pack, and positioning the heatexchanger plate within the tray such that the foam block is between thetray and the heat exchanger plate.

In a further non-limiting embodiment of any of the foregoing methods,the foam block is constructed of an expanded polymer-based material.

In a further non-limiting embodiment of any of the foregoing methods,the method includes applying a plurality of bead lines of a thermalinterface material on the heat exchanger plate, and positioning abattery array against the plurality of bead lines. Moving the batteryarray into the plurality of bead lines spreads the thermal interfacematerial between the battery array and the heat exchanger plate.

In a further non-limiting embodiment of any of the foregoing methods,applying the plurality of bead lines and moving the battery array intothe plurality of bead lines occurs after supporting the heat exchangerplate of the battery pack.

In a further non-limiting embodiment of any of the foregoing methods,the method includes curing the thermal interface material subsequent tomoving the battery array into the plurality of bead lines.

In a further non-limiting embodiment of any of the foregoing methods,the heat exchanger plate is substantially rigidly supported during theassembly process.

A battery pack according to another exemplary aspect of the presentdisclosure includes, among other things, a tray, a structural materialpositioned against the tray, a heat exchanger plate positioned againstthe structural material, a thermal interface material disposed on theheat exchanger plate, and a battery array positioned against the thermalinterface material.

In a further non-limiting embodiment of the foregoing battery pack, thestructural material is configured to maintain the heat exchanger platein a substantially flat configuration relative to the battery array.

In a further non-limiting embodiment of either of the foregoing batterypacks, the structural material is a foam block constructed of anexpanded polymer-based material.

In a further non-limiting embodiment of any of the foregoing batterypacks, a component of the battery is in direct contact with the thermalinterface material.

In a further non-limiting embodiment of any of the foregoing batterypacks, the thermal interface material is a compliant and viscousmaterial in an uncured state.

The embodiments, examples and alternatives of the preceding paragraphs,the claims, or the following description and drawings, including any oftheir various aspects or respective individual features, may be takenindependently or in any combination. Features described in connectionwith one embodiment are applicable to all embodiments, unless suchfeatures are incompatible.

The various features and advantages of this disclosure will becomeapparent to those skilled in the art from the following detaileddescription. The drawings that accompany the detailed description can bebriefly described as follows.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically illustrates a powertrain of an electrified vehicle.

FIG. 2 illustrates a battery pack for an electrified vehicle.

FIG. 3 is an exploded view of the battery pack of FIG. 2.

FIG. 4 schematically illustrates a battery pack assembly processaccording to a first embodiment of this disclosure.

FIG. 5 schematically illustrates a battery pack assembly processaccording to a second embodiment of this disclosure.

FIGS. 6A and 6B illustrate a comparison of thermal interface material(TIM) coverage for an unsupported and a supported heat exchanger plate,respectively.

DETAILED DESCRIPTION

This disclosure details exemplary battery pack designs for use inelectrified vehicles. An exemplary battery pack assembly process mayinclude supporting one or more components, such as a heat exchangerplate, of the battery pack against deflection during the assemblyprocess. Supporting the heat exchanger plate to keep the plate flatduring the battery pack assembly process improves the flow distributionof a thermal interface material (TIM), thereby achieving improved TIMcoverage and improved heat transfer between battery cells and the heatexchanger plate of the battery pack. These and other features arediscussed in greater detail in the following paragraphs of this detaileddescription.

FIG. 1 schematically illustrates a powertrain 10 for an electrifiedvehicle 12. Although depicted as a hybrid electric vehicle (HEV), itshould be understood that the concepts described herein are not limitedto HEVs and could extend to other electrified vehicles, including, butnot limited to, plug-in hybrid electric vehicles (PHEV's), batteryelectric vehicles (BEVs), fuel cell vehicles, etc.

In an embodiment, the powertrain 10 is a power-split powertrain systemthat employs first and second drive systems. The first drive system mayinclude a combination of an engine 14 and a generator 18 (i.e., a firstelectric machine). The second drive system may include at least a motor22 (i.e., a second electric machine), the generator 18, and a batterypack 24. In this example, the second drive system is considered anelectric drive system of the powertrain 10. The first and second drivesystems are each capable of generating torque to drive one or more setsof vehicle drive wheels 28 of the electrified vehicle 12. Although apower-split configuration is depicted in FIG. 1, this disclosure extendsto any hybrid or electric vehicle including full hybrids, parallelhybrids, series hybrids, mild hybrids, or micro hybrids.

The engine 14, which may be an internal combustion engine, and thegenerator 18 may be connected through a power transfer unit 30, such asa planetary gear set. Of course, other types of power transfer units,including other gear sets and transmissions, may be used to connect theengine 14 to the generator 18. In a non-limiting embodiment, the powertransfer unit 30 is a planetary gear set that includes a ring gear 32, asun gear 34, and a carrier assembly 36.

The generator 18 can be driven by the engine 14 through the powertransfer unit 30 to convert kinetic energy to electrical energy. Thegenerator 18 can alternatively function as a motor to convert electricalenergy into kinetic energy, thereby outputting torque to a shaft 38connected to the power transfer unit 30. Because the generator 18 isoperatively connected to the engine 14, the speed of the engine 14 canbe controlled by the generator 18.

The ring gear 32 of the power transfer unit 30 may be connected to ashaft 40, which is connected to vehicle drive wheels 28 through a secondpower transfer unit 44. The second power transfer unit 44 may include agear set having a plurality of gears 46. Other power transfer units mayalso be suitable. The gears 46 transfer torque from the engine 14 to adifferential 48 to ultimately provide traction to the vehicle drivewheels 28. The differential 48 may include a plurality of gears thatenable the transfer of torque to the vehicle drive wheels 28. In anon-limiting embodiment, the second power transfer unit 44 ismechanically coupled to an axle 50 through the differential 48 todistribute torque to the vehicle drive wheels 28.

The motor 22 can also be employed to drive the vehicle drive wheels 28by outputting torque to a shaft 52 that is also connected to the secondpower transfer unit 44. In a non-limiting embodiment, the motor 22 andthe generator 18 cooperate as part of a regenerative braking system inwhich both the motor 22 and the generator 18 can be employed as motorsto output torque. For example, the motor 22 and the generator 18 caneach output electrical power to the battery pack 24.

The battery pack 24 is an exemplary electrified vehicle tractionbattery. The battery pack 24 may be a high voltage traction battery thatincludes a plurality of battery arrays 25 (i.e., battery assemblies orgroupings of battery cells) capable of outputting electrical power tooperate the motor 22 and/or other electrical loads of the electrifiedvehicle 12 and are capable of receiving power from the generator 18.Other types of energy storage devices and/or output devices could alsobe used to electrically power the electrified vehicle 12, including lowvoltage batteries.

In an embodiment, the electrified vehicle 12 has two basic operatingmodes. The electrified vehicle 12 may operate in an Electric Vehicle(EV) mode where the motor 22 is used (generally without assistance fromthe engine 14) for vehicle propulsion, thereby depleting the batterypack 24 state of charge up to its maximum allowable discharging rateunder certain driving patterns/cycles. The EV mode is an example of acharge depleting mode of operation for the electrified vehicle 12.During EV mode, the state of charge of the battery pack 24 may increasein some circumstances, for example due to a period of regenerativebraking. The engine 14 is generally OFF under a default EV mode butcould be operated as necessary based on a vehicle system state or aspermitted by the operator.

The electrified vehicle 12 may additionally operate in a Hybrid (HEV)mode in which the engine 14 and the motor 22 are both used for vehiclepropulsion. The HEV mode is an example of a charge sustaining mode ofoperation for the electrified vehicle 12. During the HEV mode, theelectrified vehicle 12 may reduce the motor 22 propulsion usage in orderto maintain the state of charge of the battery pack 24 at a constant orapproximately constant level by increasing the engine 14 propulsion. Theelectrified vehicle 12 may be operated in other operating modes inaddition to the EV and HEV modes within the scope of this disclosure.

FIGS. 2 and 3 schematically depict a battery pack 24 that can beemployed within an electrified vehicle. For example, the battery pack 24could be part of the powertrain 10 of the electrified vehicle 12 ofFIG. 1. FIG. 2 is a cross-sectional view of the battery pack 24, andFIG. 3 is an exploded view of the battery pack 24 (without cover 62).

The battery pack 24 houses a plurality of battery cells 56 that storeenergy for powering various electrical loads of the electrified vehicle12. The battery pack 24 could employ any number of battery cells 56within the scope of this disclosure. Therefore, this disclosure is notlimited to the exact configuration shown in FIGS. 2-3.

The battery cells 56 may be stacked side-by-side to construct a groupingof battery cells 56, sometimes referred to as a “cell stack” or “cellarray.” In an embodiment, the battery cells 56 are prismatic,lithium-ion cells. However, battery cells having other geometries(cylindrical, pouch, etc.), other chemistries (nickel-metal hydride,lead-acid, etc.), or both could alternatively be utilized within thescope of this disclosure.

The battery cells 56, along with any support structures (e.g., arrayframes, spacers, rails, walls, plates, bindings, etc.), may collectivelybe referred to as a battery array. The battery pack 24 depicted in FIG.2 includes a first battery array 25A and a second battery array 25B thatis positioned adjacent to the first battery array 25A. Although thebattery pack 24 of FIG. 2 is depicted as having two battery arrays, thebattery pack 24 could include a greater or fewer number of batteryarrays within the scope of this disclosure. In addition, the batteryarrays 25A, 25B are shown as being positioned end-to-end. However, thebattery arrays 25A, 25B could alternatively be positioned side-by-sideor in any other configuration relative to one another. Unless statedotherwise herein, when used without any alphabetic identifierimmediately following the reference numeral, reference numeral “25” mayrefer to either battery array 25A or battery array 25B.

An enclosure assembly 58 houses each battery array 25 of the batterypack 24. In an embodiment, the enclosure assembly 58 is a sealedenclosure that includes a tray 60 and a cover 62 that is secured to thetray 60 to enclose and seal each battery array 25 of the battery pack24. In another embodiment, the battery arrays 25 are positioned withinthe tray 60 of the enclosure assembly 58, and the cover 62 may then bereceived over the battery arrays 25. The enclosure assembly 58 mayinclude any size, shape, and configuration within the scope of thisdisclosure.

Each battery array 25 of the battery pack 24 may be positioned relativeto a heat exchanger plate 64, sometimes referred to as a cold plate,such that the battery cells 56 are in close proximity to the heatexchanger plate 64. In an embodiment, the battery arrays 25A, 25B sharea common heat exchanger plate 64. However, the battery pack 24 couldemploy multiple heat exchanger plates within the scope of thisdisclosure.

The heat exchanger plate 64 may be part of a liquid cooling system thatis associated with the battery pack 24 and is configured for thermallymanaging the battery cells 56 of each battery array 25. For example,heat may be generated and released by the battery cells 56 duringcharging operations, discharging operations, extreme ambient conditions,or other conditions. It may be desirable to dissipate the heat from thebattery pack 24 to improve capacity, life, and performance of thebattery cells 56. The heat exchanger plate 64 may be configured toconduct the heat out of the battery cells 56. For example, the heatexchanger plate 64 may function as a heat sink for removing heat fromthe heat sources (i.e., the battery cells 56). The heat exchanger plate64 could alternatively be employed to heat the battery cells 56, such asduring extremely cold ambient conditions, for example. Although shown asa separate component from the tray 60, the heat exchanger plate 64 couldbe integrated with the tray 60 as a single component.

The heat exchanger plate 64 may include a plate body 66 and a coolantcircuit 68 formed inside the plate body 66. The coolant circuit 68 mayinclude one or more passageways 70 that extend inside the plate body 66.In an embodiment, the passageways 70 establish a meandering path of thecoolant circuit 68.

A coolant C may be selectively circulated through the passageways 70 ofthe coolant circuit 68 to thermally condition the battery cells 56 ofthe battery pack 24. The coolant C may enter the coolant circuit 68through an inlet 72 and may exit from the coolant circuit 68 through anoutlet 74 (see FIG. 3). The inlet 72 and the outlet 74 may be in fluidcommunication with a coolant source (not shown). The coolant sourcecould be part of a main cooling system of the electrified vehicle 12 orcould be a dedicated coolant source of the battery pack 24. Although notshown, the coolant C may pass through a heat exchanger before enteringthe inlet 72.

In an embodiment, the coolant C is a conventional type of coolantmixture, such as water mixed with ethylene glycol. However, othercoolants, including gases, are also contemplated within the scope ofthis disclosure.

In use, heat from the battery cells 56 is conducted into the plate body66 of the heat exchanger plate 64 and then into the coolant C as thecoolant C is communicated through the coolant circuit 68. The heat maytherefore be carried away from the battery cells 56 by the coolant C.

In an embodiment, the heat exchanger plate 64 is an extruded part. Inanother embodiment, the heat exchanger plate 64 is made of aluminum.However, other manufacturing techniques and materials are alsocontemplated within the scope of this disclosure.

A thermal interface material (TIM) 76 may be positioned between thebattery arrays 25 and the heat exchanger plate 64 such that exposedsurfaces of the battery cells 56 are in direct contact with the TIM 76.In an embodiment, downwardly facing bottom surfaces of the battery cells56 are in direct contact with the TIM 76. In another embodiment, thermalfins that are positioned between adjacent battery cells 56 of thebattery arrays 25 are in direct contact with the TIM 76. The TIM 76maintains thermal contact between the battery cells 56 and the heatexchanger plate 64 and increases the thermal conductivity between theseneighboring components during heat transfer events.

In an embodiment, the TIM 76 includes an epoxy resin. In anotherembodiment, the TIM 76 includes a silicone based material. Othermaterials, including thermal greases, may alternatively or additionallymake up the TIM 76.

Referring now primarily to FIG. 3, a plurality of bead lines 78 may beapplied on the heat exchanger plate 64 during assembly of the batterypack 24. Once cured, the bead lines 78 establish the TIM 76 between thebattery cells 56 of the battery arrays 25 and the heat exchanger plate64. As the battery arrays 25 are moved (i.e., pushed down) onto the beadlines 78 or the bead lines 78 are moved (i.e., pushed up) into thebattery arrays 25 during the assembly process, the bead lines 78 attemptto spread-out or distribute themselves evenly between the battery arrays25 and the heat exchanger plate 64. Prior to curing, the beads lines 78are generally viscous and compliant; however, the bead lines 78 alsoexhibit some degree of resilience and therefore may provide a resistanceforce to the distribution of the TIM 76. The resistance force may betransmitted to the heat exchanger plate 64 and cause the heat exchangerplate 64 to deflect downwardly (i.e., toward the tray 60) duringassembly. Deflection of the heat exchanger plate 64 may result in poordistribution of the bead lines 78, thereby reducing the thermaleffectiveness of the TIM 76.

It is therefore desirable to substantially eliminate the deflection ofthe heat exchanger plate 64 during the battery pack assembly process inorder to maximize the spreading distribution of the TIM 76. Exemplarytechniques for substantially eliminating deflection of the heatexchanger plate 64 during the assembly process are further discussedbelow.

FIG. 4, with continued reference to FIGS. 1-2, schematically illustratesan exemplary battery pack assembly process according to a firstembodiment of this disclosure. The heat exchanger plate 64 may bemaintained substantially flat (i.e., little to no bending) during theassembly process in order to prevent its deflection and maximizecoverage of the TIM 76. In an embodiment, a combination of supportingthe tray 60 and incorporating a foam block 80 (i.e., a structuralmaterial) into the battery pack 24 substantially eliminates deflectionof the heat exchanger plate 64.

For example, the tray 60 may be positioned against a rigid workstation82. The workstation 82 supports a bottom 84 of the tray 60. In anembodiment, the workstation 82 substantially rigidly supports the bottom84 of the tray 60. In this disclosure, the phrase “substantially rigidlysupports” means that deflection of the tray 60 and/or heat exchangerplate 64 is reduced by at least 50% during the assembly process comparedto a tray/heat exchanger plate that is not substantially rigidlysupported during the assembly process.

The foam block 80 may then be positioned within the tray 60 followed bythe heat exchanger plate 64. The foam block 80 may therefore bepositioned between the tray 60 and the heat exchanger plate 64 andsubstantially rigidly supports a bottom 86 of the heat exchanger plate64.

The combination of the rigid workstation 82 and the relatively stifffoam block 80 maintains the heat exchanger plate 64 flat during thesubsequent assembly steps in which the battery array(s) 25 arepositioned within the tray 60 and moved into contact with the bead lines78 of the TIM 76. Coverage of the TIM 76 relative to the heat exchangerplate 64 can therefore be maximized. In another embodiment, the foamblock 80 or the rigid workstation 82 can be utilized alone to rigidlysupport the heat exchanger plate 64 during the assembly process.

The foam block 80 may be constructed of an expanded polymer-basedmaterial. Exemplary expanded polymer-based materials can include, butare not limited to, expanded polypropylene, expanded polystyrene, andexpanded polyethylene. Generally, these polymer-based materials areconsidered relatively structural and stiff foamed polymer-basedmaterials. By considering the design space that is available, thedensity of the foam block 80 may be chosen such that it offers therequired stiffness for maintaining flatness of the heat exchanger plate64 during assembly.

In an embodiment, the foam block 80 is maintained within (i.e., notremoved from) the battery pack 24 after positioning the battery arrays25. The foam block 80 is therefore an integral structural component ofthe battery pack 24 upon completion of the battery pack assemblyprocess.

FIG. 5 schematically illustrates another exemplary battery pack assemblyprocess. In this embodiment, the tray 60 may be positioned against arigid workstation 82 during the assembly process. The workstation 82substantially rigidly supports the bottom 84 of the tray 60. In anembodiment, the workstation 82 includes a protruding surface 88. Theprotruding surface 88 may be a convex surface, in an embodiment. Theprotruding surface 88 may be loaded against the tray 60 to force thetray 60 into the heat exchanger plate 64 near a center of the heatexchanger plate 64 as the heat exchanger plate 64 is positioned withinthe tray 60. The protruding surface 88 maintains the heat exchangerplate 64 flat during the subsequent assembly steps in which the batteryarray(s) 25 are positioned within the tray 60 and moved into contactwith the bead lines 78 of the TIM 76. Coverage of the TIM 76 relative tothe heat exchanger plate 64 can therefore be maximized. Although notshown, the foam block 80 could additionally be used to rigidly supportthe heat exchanger plate 64 in combination with the protruding surface88 during the battery pack assembly process of FIG. 5.

FIGS. 6A and 6B illustrate a side-by-side comparison of the TIM 76coverage for a heat exchanger plate 64-U that was unsupported during thebattery pack assembly process (FIG. 6A) and for a heat exchanger plate64-S that was supported (such as in the manner shown in FIG. 4 or 5)during the battery pack assembly process (FIG. 6B). The unsupported heatexchanger plate 64-U exhibits relatively poor distribution and coverageof the TIM 76 as evidenced by the relatively large gaps G1 that extendbetween adjacent bead lines 78 of the TIM 76. In contrast, the supportedheat exchanger plate 64-S exhibits significantly improved distributionand coverage of the TIM 76 as evidenced by the reduced gaps G2 betweenthe adjacent bead lines 78 of the TIM 76. In an embodiment, the TIM 76coverage for the supported heat exchanger plate 64-S is up to 40% higherthan the unsupported heat exchanger plate 64-U.

The electrified vehicle battery pack designs of this disclosure utilizeone or more stiff materials to provide a distributed response load fromthe workstation surface, to the battery pack tray, and then to thebattery pack heat exchanger plate in order to promote a more completeflow distribution of the liquid TIM. The thermal effectiveness of theTIM is thereby improved during the life of the battery pack.

Although the different non-limiting embodiments are illustrated ashaving specific components or steps, the embodiments of this disclosureare not limited to those particular combinations. It is possible to usesome of the components or features from any of the non-limitingembodiments in combination with features or components from any of theother non-limiting embodiments.

It should be understood that like reference numerals identifycorresponding or similar elements throughout the several drawings. Itshould be understood that although a particular component arrangement isdisclosed and illustrated in these exemplary embodiments, otherarrangements could also benefit from the teachings of this disclosure.

The foregoing description shall be interpreted as illustrative and notin any limiting sense. A worker of ordinary skill in the art wouldunderstand that certain modifications could come within the scope ofthis disclosure. For these reasons, the following claims should bestudied to determine the true scope and content of this disclosure.

What is claimed is:
 1. A method, comprising: during an assembly process,supporting a heat exchanger plate of a battery pack against deflection,wherein supporting the heat exchanger plate against deflection includes:positioning a tray of the battery pack against a rigid workstation; andpositioning the heat exchanger plate against the tray, wherein the rigidworkstation includes a convex surface in contact with a bottom of thetray.
 2. The method as recited in claim 1, wherein the convex surfacecontacts the bottom of the tray near a center of the tray.
 3. The methodas recited in claim 1, comprising: applying a plurality of bead lines ofa thermal interface material on the heat exchanger plate; andpositioning a battery array against the plurality of bead lines, whereinpositioning the battery array against the plurality of bead linesspreads the thermal interface material between the battery array and theheat exchanger plate.
 4. The method as recited in claim 3, whereinapplying the plurality of bead lines and positioning the battery arrayagainst the plurality of bead lines occurs after supporting the heatexchanger plate of the battery pack.
 5. The method as recited in claim3, comprising: curing the thermal interface material subsequent topositioning the battery array against the plurality of bead lines. 6.The method as recited in claim 5, wherein supporting the heat exchangerplate includes substantially rigidly supporting the heat exchanger plateduring the assembly process.
 7. The method as recited in claim 3,wherein the plurality of bead lines are elongated and extend across asubstantial portion of a width of the heat exchanger plate.
 8. Themethod as recited in claim 1, wherein the convex surface is a protrudingsurface of the rigid workstation.
 9. The method as recited in claim 8,wherein the protruding surface forces the tray into the heat exchangerplate during the assembly process.
 10. The method as recited in claim 8,wherein the protruding surface protrudes from a substantially flatsurface of the rigid workstation.
 11. The method as recited in claim 1,wherein the heat exchanger plate is maintained substantially flat duringthe assembly process.